Chemotaxis is a fascinating biological response in which cells orient themselves and move up a chemical gradient. It is important in a variety of physiological and pathological processes including nerve growth, angiogenesis, wound healing, leukocyte trafficking, and carcinoma invasion. It is also essential for the survival of the social amoebae, Dictyostelium discoideum. During growth, these cells track down and phagocytose bacteria. When starved, they enter a differentiation program that allows the cells to survive harsh environmental conditions. They do so by chemotaxing toward secreted adenosine 3',5' cyclic monophosphate (cAMP) signals thereby forming aggregates which differentiate into spore and stalk cells. The essential role of chemotaxis in this eukaryote has provided an excellent model organism to study the biochemical and genetic basis of directed cell migration.Both leukocytes and Dictyostelium cells use G protein-linked signaling pathways to respond to chemoattractants. Binding of chemoattractants to serpentine receptors leads to the dissociation of heterotrimeric G proteins into alpha- and beta/gamma-subunits, which activate a variety of effectors that go on to produce multiple responses. These include increases in Ca2+ influx, IP3, cAMP and cGMP. Concomitantly, the level of phosphorylation of myosins I and II and polymerized actin are markedly increased. Our research program is focused on understanding how these multiple G protein-coupled signaling events are translated into directed cell migration. We have shown that a variety of signaling events are spatially restricted during chemotaxis. In one instance, this has led us to discover a novel and unexpected mechanism used by Dictyostelium cells to relay and amplify chemotactic gradients. It had been observed that these cells align in a head to tail fashion, or stream, as they migrate in a gradient of cAMP. Live imaging of ACA, the enzyme synthesizing cAMP, revealed a highly enriched localization at the plasma membrane in the rear of polarized cells. We proposed that this asymmetric distribution of ACA provides a compartment from which the chemoattractant cAMP is secreted to act locally, offering an ideal mechanism to relay chemical gradients.We are currently pursuing our studies on chemotaxis using Dictyostelium and mammalian neutrophils. As a long-term goal, we also wish to add another model, metastatic epithelial breast cancer cells, to our research program. Chemotactic agents participate in the migration of tumor cells during metastasis, providing a mechanism that explains the ability of various organs to attract specific and distinct types of cancer cells. Studies of the metastatic phenotype led to the intriguing concept that de-differentiated cancer cells revert to a primitive and efficient mode of migration shared by hematopoietic and Dictyostelium cells. The importance of amoeboid migration in a wide range of physiological and pathological events lies at the core of our research program. First, by studying cAMP metabolism in Dictyostelium, we will gain further insight into directional sensing and cell polarity events during chemotaxis, as well as decipher the cause and effect of the compartmentalization of this ubiquitous second messenger. Because of the central role of signal relay during Dictyostelium chemotaxis, this model provides an unparalleled tool to identify the mechanisms that govern collective cell migration. Second, we plan on pursuing our studies on adenylyl cyclase regulation, and the role of cAMP during neutrophils chemotaxis. In particular, we will set out to determine whether neutrophils migrate in groups as they chemotax to sites of inflammation.